The vertebrae in a patient's spinal column are linked to one another by the intervertebral disc and the facet joints. This three joint complex controls the movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface and an inferior articular surface. Together the superior and inferior articular surfaces of adjacent vertebrae form a facet joint. Facet joints are synovial joints, which means that each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing the joints to move or articulate relative to one another.
Diseased, degenerated, impaired, or otherwise painful facet joints and/or discs can require surgery to reduce pain coming from the three joint complex. In the lumbar spine, for example, one form of treatment to stabilize the spine and to relieve pain involves the fusion of the facet joint.
One known technique for stabilizing and treating the facet joint involves a trans-facet fusion in which pins, screws or bolts penetrate the lamina to fuse the joint. Such a technique has associated with it the risk of further injury to the patient as such translaminar facet instrumentation can be difficult to place in such a way that it does not violate the spinal canal and/or contact the dura of the spinal cord or the nerve root ganglia. Further, trans-facet instrumentation has been known to create a rotational distortion, lateral offset, hyper-lordosis, and/or intervertebral foraminal stenosis as the screws tend to compress the facet joint together.
Examples of facet instrumentation currently used to stabilize the lumbar spine include trans-lamina facet screws (“TLFS”) and trans-facet pedicle screws (“TFPS”). TLFS and TFPS implants provide reasonable mechanical stability, but, as noted above, they can be difficult to place, have long trajectories, and surgical access can be confounded by local anatomy. In some instances these implants can result in some degree of foraminal stenosis as the screws tend to compress the facet joints together.